Polymer blend materials composed of dispersed rigid-rod polymers, such as certain types of aromatic polyamides and a flexible polymer matrix, are gaining increased attention as new materials wherein the host matrix polymer is modified at the molecular level by the incorporation of the rigid-rod polymer in a dispersed form. Such a polymer blend material is expected to exhibit not only some of the benefits of a rigid-rod polymer as regards mechanical properties, thermal stability, resistance toward chemicals, and other properties, but also the benefits of a flexible polyamide, such as moldability. For example, improvement in tensile properties of a flexible polymer by blending a rigid-rod polymer therein has been reported. The exact definition of "rigid-rod" is given by using the term "rigid" in Japan Patent (Not examined) No. 52-131436 and U.S. Pat. No. 4,228,218. All of the polymers which are not rigid-rod ones are defined as flexible polymers. Polymer blend materials, including rigid-rod polymeric molecules dispersed at the microscopic level, are of great interest as novel materials for many applications.
However, it is commonly difficult to disperse one polymer in another polymer. Phase separation or aggregation thermodynamically inevitable. Several efforts have been examined to overcome the difficulty of blending rigid-rod polymers with flexible polymers. A coagulation method is conventionally employed for the preparation of polymer blend materials which include a rigid-rod polymer. In this method, a homogeneous solution including a rigid-rod polymer and a flexible polymer are put rapidly into a poor solvent, resulting in a precipitate of polymer blend materials. The coagulation process is insufficient to achieve the fine dispersion of rigid-rod polymers because entropy-driven demixing might take place during coagulation even though nonequilibrium solidification is expected.
As for polymer blend materials composed of poly(p-phenyleneterephthalamide) [PPD-T] and nylon, which are of concern in the present invention, the formation of 30 nm-diameter microfibrils of PPD-T are observed for blends of PPD-T/nylon obtained by a coagulation method as is previously reported in J. Macromol. Sci. Phys., B17(4), 591 (1980).
Moreover, a coagulation method involves another disadvantage. A rigid-rod polymer such as poly(p-phenyleneterephthalamide) [PPD-T] usually requires strong acids as solvents due to its poor solubility. To prepare homogeneous solutions, a large amount of strong acid solvent, e.g., sulfuric or methanesulfonic acid, must be employed. However, the use of strong acids induces polymer degradation and is not economical for obtaining a large amount of polymer blend materials, especially for industrial processes.
Alternatively, a comparatively new method of blending a rigid-rod polymer in a matrix polymer is known wherein the rigid-rod polymer is synthesized in situ in the presence of the matrix polymer.
In these methods, rigid-rod polymers are synthesized in a dissolved or molten matrix of flexible polymer. For example, Ogata et al. synthesized rigid-rod polyamides such as PPD-T and PBA [poly(p-benzamide)] and rigid-rod polyesters such as PHB [poly(p-hydroxybenzoate)], etc., in the presence of matrix polymers such as polyarylate and elastomers dissolved in chlorohydrocarbons etc., which, however, resulted in a suspension of rigid rod polymer, resulting in opaque films containing large aggregations of 500 nm or more, as is described in Polym. J., 22(2), 85 (1990), Chem. Mater. 4, 1123 (1992), J. Polym. Sci., Part A: Polym. Chem., 31, 597 (1993). Rosch reported that a mixture of PBA and PABC [poly(p-aminobenzoyl- caprolactam)] was formed in situ in a nylon matrix, resulting in a phase separated structure between nylon 6 and PBA/PABC [Polym. Prepr. 33(1), 370 (1992)]. It is true that these attempts are considered to be advantageous in that conventional aprotic solvents or no solvent is employed to produce polymer blend materials including rigid-rod polymers, but such observations led to the conclusion that no fine dispersion of rigid-rod polymers at a nanometer level was obtained which thereby brings about poor transparency.
It is obvious that even with these methods, including the in situ methods conventionally employed to date, entropy driven demixing of polymers occurs to some extent. A production method of the polymer blend materials including rigid-rod polymers without using strong acids and giving uniformly dispersed forms of aromatic polyamides therein has not been established and such systems are still desired.
The present invention relates to polymer blend materials produced by in situ synthesis of a rigid-rod polyamide through the phosphorylation polycondensation reaction in the presence of a soluble polyamide. The phosphorylation polycondensation reaction in the presence of a dissolved polymer matrix has been previously reported as follows. The synthesis in a poly(4-vinylpyridine) matrix and a poly(ethyleneoxide) matrix, respectively, has been described in Journal of Polymer Science: Polymer Chemistry Edition, Vol. 18, 851 (1980), and Journal of Polymer Science: Polymer Chemistry Edition, Vol. 18, 1099 (1980). The synthesis in the matrices of poly(vinylpyrrolidinone), poly(4-vinylpyridine) and poly(ethyleneoxide) has been described in Journal of Polymer Science: Polymer Chemistry Edition, Vol. 18, 2875 (1980).
However, these methods are quite different from the present invention. In particular, polyamides are not employed as matrix polymers, the matrix polymers are merely employed as reaction promoters to produce high-molecular-weight aromatic polyamides, and improved transparency and improved resistance toward chemicals of resultant polymer blend materials over the starting matrix polymers, which were discovered in the present invention, are not mentioned. Additionally, transparent gel formation during the synthesis and fine dispersion of the synthesized aromatic polyamides in the matrix polymers, which were discovered in the present invention, are not mentioned. Furthermore, the polymers which are employed are water soluble, and therefor do not remain in the final product.
The above mentioned in situ reaction was conducted by using N-methyl-2-pyrrolidinone ("pyrrolidinone" is also referred to as "pyrrolidone") as a solvent suitable for the phosphorylation reaction and capable of dissolving the matrix polymers. Although it is known that polyamides such as nylon 6 could dissolve in amide type solvents at the boil such as N-methyl-2-pyrrolidinone as was described in U.S. Pat. No. 2,958,677, however, the in situ synthesis through the phosphorylation reaction in the presence of polyamides such as nylon 6 has not been examined.
It should be mentioned that the present invention is mainly aimed towards a polymer blend material composed of a rigid-rod aromatic polyamide and a flexible aliphatic polyamide. However, the present invention is found to be effective also for a polymer blend material from a nonrigid-rod aromatic polyamide and a polyamide which is simply soluble in a certain solvent. Therefore, in a broad sense, the present invention relates to a polymer blend material comprising an aromatic polyamide and a soluble polyamide as the title indicates.